It is an object of the present invention to provide emulsion-polymerized latex products which can be used in formulation with pigmentary materials to provide water-based paints which have superior wet primed adhesion, i.e. paints which, after being coated over a surface of alkyd primer and dried, have a superior adhesion to the alkyd surface when subsequently exposed to water.
It is a further object of this invention to provide such latex products at minimum cost by preparing the polymers therein from monomers comprising a major amount of monomers selected from the low-cost vinyl acetate and vinyl chloride.
The market for water-based paints, containing emulsion polymerized latexes as binders, is constantly growing in preference over oil-based paints which contain organic volatile components having undesirable properties such as odor and flammability. For some applications, particularly indoor applications, it has been found satisfactory to use as the latex binder for such water-based paints, an emulsion copolymer comprising a major amount of vinyl acetate or vinyl chloride, thus effecting substantial economies.
However, a corresponding use of vinyl acetate or vinyl chloride in outdoor water-based paints has not met with equal success. When wood clapboards or shingles, for example, are first primed with a conventional exterior alkyd undercoat and then painted with a water-based paint, it is not unusual to find that the initially attractive coating soon deteriorates during repeated exposure to rainy weather. The imbibition of water at the primer/topcoat interface results in blistering and peeling.
In short, previous attempts to use latex copolymers containing polymerized therein a major portion of vinyl chloride or vinyl acetate as binders for exterior paints have resulted in products which were deficient in wet primed adhesion. This deficiency was not overcome by copolymerization with up to 5%, based on total main monomers, of a carboxylated monomer or an ethylenically unsaturated amide, or both. Thus, for example, a polymer of 70 parts vinyl chloride, 30 parts 2-ethyl hexyl acrylate plus up to 5 parts acrylic acid and/or up to 5 parts acrylamide, methacrylamide or N-methylolacrylamide does not achieve wet primed adhesion. Likewise unsuccessful in the hands of present Applicants, have been polymers containing polymerized therein 70 parts vinyl acetate, 30 parts 2-ethyl hexyl acrylate, up to 5 parts of acrylic acid and/or up to 5 parts of acrylamide or its lower alkyl or hydroxyalkyl derivatives.